From 6a7e6f78c235975cc14d4e141fa088afffe7062c Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Thu, 30 Mar 2017 15:39:34 +0200 Subject: [PATCH] tty: close race between device register and open The tty class device is currently not registered until after the character device has been registered thereby leaving a small window were a racing open could end up with a NULL tty->dev pointer due to the class-device lookup failing in alloc_tty_struct. Close this race by registering the class device before the character device while making sure to defer the user-space uevent notification until after the character device has been registered. Note that some tty drivers expect a valid tty->dev and would misbehave or crash otherwise. Some line disciplines also currently dereference the class device unconditionally despite the fact that not every tty is guaranteed to have one (Unix98 pty), but this is being fixed separately. Signed-off-by: Johan Hovold Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 40 ++++++++++++++++++++-------------------- 1 file changed, 20 insertions(+), 20 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index de4543ee290b..8e9651579d50 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -3293,9 +3293,8 @@ struct device *tty_register_device_attr(struct tty_driver *driver, { char name[64]; dev_t devt = MKDEV(driver->major, driver->minor_start) + index; - struct device *dev = NULL; - int retval = -ENODEV; - bool cdev = false; + struct device *dev; + int retval; if (index >= driver->num) { pr_err("%s: Attempt to register invalid tty line number (%d)\n", @@ -3308,18 +3307,9 @@ struct device *tty_register_device_attr(struct tty_driver *driver, else tty_line_name(driver, index, name); - if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) { - retval = tty_cdev_add(driver, devt, index, 1); - if (retval) - goto error; - cdev = true; - } - dev = kzalloc(sizeof(*dev), GFP_KERNEL); - if (!dev) { - retval = -ENOMEM; - goto error; - } + if (!dev) + return ERR_PTR(-ENOMEM); dev->devt = devt; dev->class = tty_class; @@ -3329,18 +3319,28 @@ struct device *tty_register_device_attr(struct tty_driver *driver, dev->groups = attr_grp; dev_set_drvdata(dev, drvdata); + dev_set_uevent_suppress(dev, 1); + retval = device_register(dev); if (retval) - goto error; + goto err_put; + + if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) { + retval = tty_cdev_add(driver, devt, index, 1); + if (retval) + goto err_del; + } + + dev_set_uevent_suppress(dev, 0); + kobject_uevent(&dev->kobj, KOBJ_ADD); return dev; -error: +err_del: + device_del(dev); +err_put: put_device(dev); - if (cdev) { - cdev_del(driver->cdevs[index]); - driver->cdevs[index] = NULL; - } + return ERR_PTR(retval); } EXPORT_SYMBOL_GPL(tty_register_device_attr); -- 2.20.1